Horizontal-axis wind turbines for generating electricity from rotational motion are generally comprised of one or more rotor blades each having an aerodynamic body extending outwards from a horizontal shaft that is supported by, and rotates within, a wind turbine nacelle. The rotor blades are examples of structures adapted to traverse a fluid environment, where the environment is primarily ambient air. The nacelle is supported on a tower which extends from the ground or other surface. Wind incident on the rotor blades applies pressure causing the rotor blades to move by rotating the shaft from which they extend about the horizontal rotational axis of the shaft. The shaft is, in turn, associated with an electricity generator which, as is well-known, converts the rotational motion of the shaft into electrical current for transmission, storage and/or immediate use. Horizontal-axis wind turbines are generally very well-known and understood, though improvements in their operation to improve the efficiency of power conversion and their overall operational characteristics are desirable.
Incident wind at even low speeds can cause the rotor blades to rotate very quickly. As would be well-understood, for a given rotational velocity, the linear velocity of a rotor blade is lowest in the region of its root—the portion of the rotor blade proximate to the shaft. Similarly, the linear velocity of the rotor blade is highest in the region of its wingtip—the portion of the rotor blade distal from the shaft. Particularly at higher linear velocities, aspects of the rotor blade can generate significant aeroacoustic noise as the rotor blade rapidly “slices” through air along its rotational path. This noise can be quite uncomfortable for people and animals in the vicinity to witness. However, the noise can also be an indicator that operation is not efficient, and maximum wingtip speed can actually be limited by such inefficiencies.
Horizontal-axis wind turbines are comprised of at least two and typically three rotor blades. The total swept path of the rotor blade(s) is considered to be the measure of the total kinetic energy available to the wind turbine in that plane. Current wind technologies are able to extract only a fraction of the kinetic energy of the incident wind. The maximum theoretical value of kinetic energy extraction from the wind—which is known as the Betz Limit—was demonstrated in 1919 by Albert Betz according to a principle known as Betz's Law. According to Betz's Law, the maximum coefficient of performance (Cp) in wind kinetic energy extraction, the Betz Limit, is 59.3%.
Current wind technologies have, in reality, a much lower Cp than the Betz Limit. Efficiencies of wind turbines have been increasing in recent years, mostly through advances in rotor blade designs. However, some nascent research has begun to explore the utilization of wind incident in the central hub portion in front of the plane of rotor blade travel to improve efficiency and yield and decrease noise emissions.
The portion in front of the central hub where the rotor blade(s) are attached may or may not be covered by a nose cone. The nose cone commonly acts as a protective shield for the hub of a wind turbine. To date, nose cones are not generally configured to aid in rotating the shaft of the wind turbine or to act in any way to produce energy. To this end, it is a common understanding that the total swept path of the rotor blade(s) is considered to be the measure of the possible kinetic energy available to the wind turbine in that plane and that the kinetic energy of the wind in upstream of the wind turbine hub is currently under-utilized.
European Patent Application No. EP2592265 to Orbrecht et al. discloses a power producing spinner for a wind turbine. This application describes an area for airfoil extension over the root area of the rotor blade(s), connecting at the hub region and an upwind airfoil portion disposed upwind of an inboard portion of each blade of the wind turbine; the wind turbine having a plurality of blades interconnected about an axis of rotation by a hub. The patent application further describes the ability of the power producing spinner to increase the efficiency of the wind turbine by increasing an axial induction to air flowing over the power producing spinner and directing an air flow outboard to aerodynamically useful regions of the blades.
U.S. Pat. No. 8,287,243 to Herr et al. discloses a spinner of a wind turbine. The air-flow in an inner rotor section may pass the rotor of the wind turbine without being used for energy production. A cylindrical spinner deflects wind around the rotor blade root(s) so that there is an increase in the efficiency of an existing wind turbine.
The control of yaw of a wind turbine is important to maintain maximal efficiencies, by containing wind incident to roughly 90 degrees from the spinning of the rotor blades. Currently, this is achieved via active systems that reside at the base of the nacelle at the point of connection with the tower, as in U.S. Pat. No. 7,944,070 to Rosenvard et al. and U.S. Pat. No. 8,899,920 to Anderson. These active systems are controlled by sensors located on the exterior of the nacelle at the rear portion from first wind incident. Thus, these sensors are informed of wind conditions, most importantly speed and direction, after the wind has passed by the rotor blades. As such, there is a delay in the information of wind speed and direction to the active yaw system at the base of the nacelle.
European Patent Application Publication No. EP 2048507 to LeClair et al. discloses sensors located on the front of a nosecone. However, the sensors send their information to an active systems of motors and gears that are not able to actively move the turbine such that maximal efficiencies are generated without a feedback loop and subsequent delay. Furthermore, these systems similarly require electrical power to operate.
Traditional nose cones are attached to the hub through a spinner. The spinner may then be attached to the hub through several methods including struts and having its form wrap around the root(s) of the rotor blade(s) to secure it in place. Most of these methods require the blades to not be present for spinner attachment, which may be fine for assembling a new wind turbine but can be time consuming and costly for retrofitting an operating turbine.
It is well known that the hubs and nacelles of a wind turbine require ventilation due to the heat that is created within them. Many techniques are known to ventilate the air within these structures.
Surface textures have also been known to improve the laminar flow over objects. These textures are often self-similar and repeating in nature. These may be recessed into the form, or project out of the form, and/or may also be U-shaped or V-shaped troughs that swerve or zig-zag in beneficial ways, or vortex generators that extend out of the form.